1. Field of the Invention
The present invention relates to a blood component-separating composition (hereinafter referred to as "blood separation composition") which is employed in a centrifugal separation method to separate serum or plasma from whole blood, wherein the difference in specific gravity between them is utilized.
2. Prior Art
Many kinds of blood separation compositions which have been proposed are useful in the centrifugal method of blood separation. Those prior art separation compositions contain as their main ingredient a gel-like material such as silicone oil, a chlorinated poly-butane, an acrylic polymer or a copolymer of an .alpha.-olefin and a diester of maleic acid. Typical additives blended with the main ingredient are a thixotropic agent for enhancing important properties of the gel-like material; and an inorganic substance. The thixotropic agent causes the gel-like material not to flow within the blood collection tubes but to stay on bottom of the tubes while being transported. When centrifugal force is applied to the collection tubes filled with blood, the gel-like material moves upwards and forms a partition barrier between the serum (or plasma) and the clot. The thixotropic agent also enhances the strength and stability of the partition barrier. On the other hand, an inorganic substance such as titanium dioxide and calcium carbonate is blended with the gel-like material so as to adjust its specific gravity.
However, the prior art gel-like materials are disadvantageous in that it is not easy to adjust the viscosity and specific gravity to the levels desirable for a blood separation composition. Consequently, it has been necessary to add to the gel-like material a large quantity of a thixotropic agent and/or a specific density-adjusting agent, with the former agent adjusting the thixotropic property of the blood separation composition. Thus, the actual specific gravity of the blood separation composition cannot be kept at a constant level but varies among production lots thereof and over the course of time. In addition, fractions of the separation composition are likely to be dispersed in the serum phase (or plasma phase) which will be obtained by the centrifugal separation of blood samples. Said fractions will form an oily substance which floats in the serum or plasma and is likely to clog the nozzles in an automatic analyzer. Further, because of insufficient strength of the partition barrier, perfect centrifugal isolation of the serum (or plasma) from the clot is not ensured. A number of blood cells will remain in the serum phase above the partition, thus impairing the separation accuracy.